Sensitive SQUID magnetic field sensors will be used to study the magnetic field of the human brain evoked by visual stimuli. This neuromagnetic research has two general objectives: first, to gain insight into the properties of the visual system that are significant for perception; and second, to evaluate the information provided by the magnetic field pattern concerning the physiological nature of the source. The neuromagnetic results will be compared with the more traditional measures of evoked scalp potentials. Visual stimuli will consist of grating patterns that can be varied in spatial frequency, luminance, contrast, and the rate at which the contrast is reversed to evoke a steady state response. The amplitude of the component of the field normal to the scalp as well as the phase lag of the response will be mapped for various sets of stimulus parameters. The variation in amplitude and latency will be comprised with psychophysical measures of sensitivity and reaction time.